Anthrax is a significant pathogen of wild and domestic animals and remains of concern of humans exposed to the organism or its spores. The spores in particular constitute the major health threat as they are highly stable, persistent once released to the environment, infectious by inhalation, and produce severe systemic pathology. The exotoxin of anthrax is composed of three genes; protective antigen (PA), lethal factor (LF) and edema factor (EF). It is the PA protein that binds to eukaryotic cell receptors and mediates the function of either LF or EF and thus is the critical component of the toxin. The gene for PA has been cloned in E. coli but expression from its native promoter is low. PA has also been shown to induce immunity to anthrax infection and forms the major component of the acellular human vaccine. However live vaccines studied in animals provide broader and longer lasting protection. The objective of this proposal is to determine whether or not increased immune response can be achieved with live prototypic vaccines that are engineered to overproduce PA. The experimental approach will utilize subcloning of the PA gene into an inducable T7 expression system, transformation of E. coli and B. subtilus and administration of prototypic live vaccines to rats. Prototypic vaccines will be generated from induced (overexpressed) and non-induced (native) recombinants and comparisons made of PA antibody titers by ELISA. This approach will provide evidence for the enhancement of the immune response potentiated with live prototypic overproducer vaccines to anthrax. The method may also have application to other vaccine development.